The present invention generally relates to wireless communication networks, and particularly relates to improved closed-loop power control through more accurate estimation of signal-to-noise ratios for received signals.
Most wireless networks employ power control to control the transmit power of both base stations and mobile stations. At base stations, forward link power control ideally limits the transmit power directed to individual mobile stations to the levels needed to achieve minimally acceptable received signal quality at each of the mobile stations. Transmitting to a mobile station at a power above the level needed to achieve acceptable received signal quality wastes the limited total transmit power at the base station, thereby reducing its capacity to serve the greatest possible number of mobile stations, and unnecessarily increases interference at surrounding base stations. Similarly, mobile stations transmitting with excess power on the reverse link unnecessarily wastes power at the mobile stations, and undesirably raises the “noise floor” at the base station.
In a common approach to forward link power control, mobile stations provide power control feedback to transmitting base stations. Such feedback depends on received signal quality at the mobile stations. Each mobile station transmits power control commands to one or more supporting base stations, such that forward link transmit power is maintained at approximately the level required to a targeted received signal quality at the mobile station, even during dynamically changing reception conditions.
Any inaccuracy in the mobile station's determination of received signal quality manifests itself in inaccurate forward link transmit power control. For example, if the mobile station underestimates the signal-to-noise ratio (SNR) of the received signal, its comparison of the estimated SNR with the target SNR may suggest a greater than actual shortfall in received signal quality. Consequently, the mobile station may request more transmit power from the base station than necessary to meet the targeted signal quality. The amount by which requested transmit power exceeds the actual power needed represents an inefficiency because the wasted power could otherwise be used to support additional mobile stations.